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FAQs on the Ongoing Gulf of Mexico Dolphin Die-off
An Unusual Mortality Event (UME) is defined under the Marine Mammal Protection Act as a stranding that is unexpected, involves a significant die-off of any marine mammal population, and demands immediate response. There are seven criteria used to determine whether a mortality event is "unusual." If the Working Group on Marine Mammal Unusual Mortality Events (WGMMUME), a group of marine mammal health experts, determines that an event meets one or more of the criteria, then an official UME is declared.
19 UMEs have occurred in the Gulf of Mexico (12 of which involved cetaceans; the remaining 7 were specific to manatees only) since 1991, when the marine mammal UME program was established. More information on UMEs is available on our website.
- In the majority of previous dolphin mortality events in the Gulf, either morbillivirus or brevetoxicosis were suspected or confirmed as causal factors. Evidence to date does not support either morbillivirus or brevetoxicosis as a cause of the current UME
- Identification of spatial, temporal, and demographic clusters within the UME suggest that this mortality event may involve different contributing factors varying by location and time including a contributing role of the DWH oil spill on increased dolphin mortality following the spill.
- Current results available from the UME investigation can be found on our results page
How many dolphins have stranded in the UME?
A total of 1141 cetaceans have stranded during the UME. Please see the Northern Gulf of Mexico UME website for details . Please note the numbers listed are preliminary and may be subject to change. Since not all cetaceans that have died will wash ashore and be found, the number reported stranded is likely a fraction of the total number of cetaceans that have died during the UME.
In general, throughout the region, strandings have been high for all age classes of dolphins. While it is typical to see a peak in strandings of premature, stillborn, and neonatal dolphins (<115cm) in the spring in the northern Gulf of Mexico, the peak observed in 2011, particularly in Mississippi and Alabama, was particularly high.
What other studies are going on to assess the effects of the Deepwater Horizon BP oil spill on marine mammals?
Shortly after the oil spill response was initiated, the Natural Resource and Damage Assessment (NRDA) process for marine mammals began (early May 2010). Under the NRDA, a variety of studies have been conducted to determine potential impacts from the spill on marine mammals. Please see the Final Programmatic Damage Assessment and Restoration Plan and Final Programmatic Environmental Impact Statement.
Where can I find additional information on UMEs?
- Northern Gulf of Mexico UME
- Participants in NOAA's National Marine Mammal Stranding Network
- Marine Mammal UMEs
- National Contingency Plan for Response to Unusual Marine Mammal Mortality Events [pdf]
- Working Group for Marine Mammal UMEs
Updated: May 26, 2016